Generators for producing electricity are well known and have been commercially available for many years. These devices typically include an internal combustion engine. They are adapted to provide alternating current (AC) electricity, through a standard two-prong or three-prong plug receiver, at 120 or 240 volts, and at 50 to 60 Hz; also common is an additional 12 volt DC power port for charging lead acid batteries. Devices which use either gasoline-only or heavy fuels only, such as JP-8, diesel fuel, jet fuel or kerosene, are available.
Gasoline has a low-flashpoint (less than −20° C.) and high autoignition temperature (greater than 200° C.). In operation gasoline requires the proper air to fuel ratio and a spark to induce and maintain ignition. A throttle and/or fuel injector is used to meter the fuel/air mixture which is sucked into the cylinders of the engine during operation. The low flashpoint and volatility of gasoline allows starting of the spark ignition engine at temperatures below freezing, allowing for operation over a broad range of temperatures typically between −20° C. to 55° C. In order to obtain acceptable efficiency, a compression ratio of 8:1 to 12:1 is desirable for a gasoline-only engine, which is low enough to allow for manual pull-starting of the engine and the construction of simple lightweight portable engine devices made of aluminum.
Portable gasoline generators have a simple design in order to keep them light, low cost and durable. Such devices include an engine having a carburetor (which is part of a throttle assembly) for mixing air and fuel, and do not include a fuel injector. A carburetor main jet controls the maximum amount of fuel present in the air-fuel mixture exiting the throttle assembly, and a choke is used to reduce the amount of air in the air-fuel mixture, for starting the engine.
A small portable generator which could be operated on both gasoline and heavy fuels, such as JP-8, was recently developed (hereinafter referred to as a “flexible fuel generator”): see International Application Publication No. WO 2013/103542. This generator includes an engine, and is similar to a small portable gasoline generator, but has been designed to operate at a temperature range of 120-180° C. The device also includes a start module which delivers a small amount of a low-boiling point low-flashpoint fuel to the throttle assembly via the air intake, for starting the engine when using a pull-start. This generator is intended for use in remote field locations, where gasoline may not be readily available.
A choke valve is sometimes installed in the carburetor of internal combustion engines. Its purpose is to restrict the flow of air, thereby enriching the fuel-air mixture while starting the engine. Depending on engine design and application, the valve can be activated manually by the operator of the engine (via a lever or pull handle) or automatically by a temperature-sensitive mechanism called an autochoke. Choke valves are important for naturally aspirated gasoline engines because small droplets of gasoline do not evaporate well within a cold engine. By restricting the flow of air into the throat of the carburetor, the choke valve reduces the pressure inside the throat, which causes a proportionally greater amount of fuel to be pushed from the main jet into the combustion chamber during cold-running operation. Once the engine is warm (from combustion), opening the choke valve restores the carburetor to normal operation, supplying fuel and air in the correct stoichiometric ratio for clean, efficient combustion. (From en.wikipedia.org/wiki/Choke_valve, last updated 26 Oct. 2015.)
Since use of a choke when starting the engine enriches the fuel-air mixture with fuel, undesirable noxious or toxic substances emitted from the exhaust of the engine, such as carbon monoxide (CO) from incomplete combustion, hydrocarbons from unburnt fuel, nitrogen oxides (NOx) from excessive combustion temperatures, and particulate matter (mostly soot) are much greater than what is typically emitted by the engine after the engine has warmed up and the choke valve restored restores the carburetor to normal operation.
Note that the term “choke” is applied to the carburetor's enrichment device even when it works by a totally different method. Commonly, SU carburetors have “chokes” that work by lowering the fuel jet to a narrower part of the needle. Some others work by introducing an additional fuel route to the constant depression chamber. Chokes were nearly universal in automobiles until fuel injection began to supplant carburetors. Choke valves are still common in other internal-combustion applications, including most small portable engines, motorcycles, small propeller-driven airplanes, riding lawn mowers, and normally aspirated marine engines. (From en.wikipedia.org/wiki/Choke_valve, last updated 26 Oct. 2015.)